Electric heater



@ct. 24, 1939. T. E. DADSON 2177x173 ELECTRIC HEATER Filed March 23.1936 2 Shasta-Sheet 1 *1 INVENTOR 7 2017145 .Zfwban ATTORNEY PatentedOct. 24, 1939 PATENT OFFICE ELECTRIC HEATER Thomas E. Dadson, Royal Oak,Mich., assignor to Electromaster, 1110., Detroit, Mich., a corporationof Michigan Application March 23,

3 Claims.

This invention relates to electric heaters and more particularly toheater units especially adapted for electric cooking stoves.

Heaters of this nature are generally so built and assembled into thesupporting stove structure that they may be readily removed andreplaced. In recent years there has been a marked tendency towards usingas the support, the panel forming the top of the stove.

It is one of the objects of my invention to devise a novel connecting orattaching mechanism whereby the heater unit, although readily removable,may yet be firmly held against accidental displacement from itsoperating position.

Heater units for this purpose generally com prise a refractory platetowhich is affixed one.

or more spirally wound'helices of resistance wire. The plate generallyconsists of baked clays or other frangible relatively inflexiblematerials. It is carried by a base plate usually of metal which in turnserves as the physical connection and support between the refractoryandthe top panel of the stove. Covers for the refractory, usually madeof sheet metal, have been proposed in order to protect it and theheating wire against mechanical injury, or discoloration and spoilagedue to the spilling of the materials being heated. Such covers have inthe past presented several problems which my present invention solves.

One of the objects of my invention is to design a cover for enclosing afrangible refractory plate, which may be attached to the base in such away that substantially no cooking utensil load can be applied to therefractory.

Another object of my invention is to devise a mounting for a frangiblerefractory plate, in an enclosed.heating unit, in which the plate issecurely held against displacement with respect to the enclosure and yetis still free to expand or contract under the. influence of heat withoutbeing subjected, particularly at its perimeter, to loads of the bendingtype, or to shocks from the cooking utensils.

A still further object of my invention is to provide an enclosed heaterunit in which, under the influence of temperature changes, thedistortion of the several parts of the heater will be controlled so thatthe heater may remain serviceable over a long period of time.

Another object of my invention is, to design a mounting for a heatercover whichwill tend to prevent buckling or warping of the top of thecover.

Another object of my invention is to provide a 1936, Serial No; 70,329

heater cover pre-formed to a distorted shape, which may be deformed wheninstalled in such a way as to pre-load. the cover,.the deformingstresses set up in the cover serving -to counterbalance heat stresses.

Another object of my invention is to provide a refractory member of thetype described having an extremely low mass.

Another object of my invention is to provide a heater unit mounting inwhich the unit may be yieldably held against displacement with respectto its support and at the same time be slightly spaced therefrom so thatthere may be a minimum of heat transferred from the unit to the support.

Other objects and advantages of this invention will appear in thefollowing description and appended claims, reference being had to theaccompanying drawings forming a part of this specification wherein likereference characters designate corresponding parts in the several views.

In the drawings:

Fig. '1 is a plan view of a portion of a stove top having a heater unitwhich incorporates my invention, portions of the unit being cut awaymore fully to disclose the invention.

Fig. 2 is a sectional view through the cover and the stovetop taken onthe line 22 of Fig. 1.

Fig. 3 is an enlarged sectional view of a portion of Fig. 1 taken on theline 33 thereof.

Fig. 4 is an enlarged sectional view of a portion of the heater unittaken on the line 44 of Fig. 2. Fig. 5 is a bottom plan view of theheater unit.

Fig. 6 is a section taken on the line 66 of Fig. 1 and illustrating anenlarged fragmentary view of a portion of-the refractory plate andheating wire; and

Fig. 7 is an enlarged view of Fig. '1 taken on the line 'l'| thereof andillustrating particularly a portion of the heater unit supportingmechanism.

Referring to the drawings, l0 illustrates the top panel of a flat toppedstove in which has been mounted a heater unit of the enclosed type. Theunit in general comprises a sheet metal base plate II, a refractoryplate I! carried thereby, a sheet metal cover l3, heater elements 14 andi6, and electrical connections and supports to be described.

The base member ll comprises a central disc or plate portion having anindentation I! in the center thereof, in which may be located areinforcing disc I 8 spot welded, or otherwise integrally securedthereto. The base and reinforcing discs are provided with a plurality ofaper tures l9, arranged diametrically thereof, and a centrally locatedaperture 2|.

Integrally formed with the base is an upstanding flange 22 extendingcircumferentially thereof, the top portion of the flange being bent toprovide an annularly extending portion 23 and a depending lip 24 aroundthe perimeter of the portion 23. At spaced intervals around the flange24, suitable lugs 26 may be provided for carrying the weight of theheater unit.

Attached to the base H at points spaced circumferentially thereof, andpreferably diametrically opposed, are a pair of leaf spring fingers 21having a laterally extending portion 28 and an upstanding portion 29.

The base of the heater unit and the parts associated therewith, to bedescribed, are arranged within a recess in-the top panel 10, the side ofthe recess being deformed to provide a flange 3| and a shoulder 32substantially parallel to the top of the panel.

The shoulder 32 provides a. ledge portion on which the lugs 26 may rest.Spaced circumferentially of the shoulder, at positions opposite thespring fingers 21. is a pair of notches 33. The distance between theouter portion or base of the notches is arranged to be slightly lessthan that between the ends of the laterally extending portions 28 of thespring fingers. Thus when the heater base is in place, the springfingers are bent slightly from the vertical as shown in Fig. '7. Thespring tension thus induced thereby holds the unit with the lugs 26 incontact with the shoulder 32. The sides of the notches, which engage therides of the upstanding portions of the spring fingers prevent rotationof the heater unit.

The unit may be installed by first engaging the upstanding portion 29 ofone spring finger 21 with the bottom of its notch 33, the heater unitbeing tilted downwardly on this side as far as it can go. This makes itpossible, by applying pressure to the other side of the unit, tocompress the inserted spring finger 21 so that the laterally extendingportion 28 of the other spring will snap past the shoulder 32. Theheater may be removed by reversing this procedure.

Attached to the bottom of the-base is a bracket 34 in which is mounted arefractory or insulating member 36 having hollow studs 31 extendingthrough openings in the bracket. Through these studs extends anelectrically conducting member 38 bolted as at 39 to the stud and thusaxially fixed therein. One end of the stud is electrically connected, asby the connectors 4| to the power line and the other end may beconnected to the ends 42 of the heating or resistance wires 43.

Inside the cup-shaped base formed. by the flange 22 and the base portionII, is a series of lugs 44 spaced circumferentially of the base. Asshown, these lugs are angular strips of metal of uniform width. One legis aflixed to the flange 22, the other extending-radially of the baseand in contact therewith for a purpose to be described.

The refractory plate I2 comprises a body having an extended uppersurface in which is located a pair of spiral grooves 41, the lead of thespiral beingf'sufficiently great so that the two grooves may be nested.Within the grooves are the heating wires 43 shown as being of helicalform. The material of the refractory plate forming the bottom of thegroove 41 is punched up:

wardly during the forming process to provide a lug 48 for retaining theheating wire in place.

As shown, the spiral grooves are arranged with their inner and outerends substantially 180 apart.

The refractory plate, as above indicated, is of fire brick material orbaked clay capable of withstanding the high temperatures encountered inelectric cooking. This material is frangible or inelastic and issubstantially incompressible, and has a low coeflicient of heatexpansion. It is chosen chiefly for its ability as a non-conductor bothof heat and electricity. The top surface of the plate is slightly convexfrom the center outwardly so that the height oi. the ridges 49 betweenthe grooves, progressively decreases radially of the plate. At thecenter of the plate is a bore 52 having a substantially cylindricalportion extending upwardly for about half the thickness of the plate. Atthis point the bore is formed into a conical portion 54 which extendsnearly to the top of the plate where the bore becomes again cylindricalas at 56. There thus is formed a plane annular section 5| extendingaround the bore.

The outer perimeter of the refractory plate is cut away radiallyadjacent the outer end of each spiral to expose the inner spiral. Thisforms an outer perimeter conforming to the outer portions of each of thespirals. ,In this way the mass of the plate is still further reduced ascompared with a similar plate having a circular perimeter. Thismaterially contributes toward the heating speed and efiiciency. Bosses51 integral with the plate extend downwardly through the openings 19 inthe base H, there being apertures in these studs through which the endsof the resistance wires 42 are led to the studs 38. I

The cover plate 13 comprises a centrally located annulus -or loadreceiving portion 58 and a depending flange portion 59 of lessdiameterand height than the flange 22 on the base. The annular portion58 of the cover is slightly dished or convex upwardly and before beingapplied to the heaing unit asumes the shape indicated in dotted lines at'6l. At the middle of the plate is a truncated conical recess 62 havinga shoulder 63. The angle of the conical portion 62 is less than theangle of the conical portion 54 in the refractory plate. Thus the coverwill not pro duce a wedging action against the top of the bore 52 andthere will be no tendency to disrupt the refractory plate.

'Located within the bore '52 is a sleeve member. 64 which bears againstthe base reinforcing member l8 and extends upwardly towards the shoulder63 on the cover plate.

The sleeve is externally threaded: On the exterior is a refractoryretaining nut 66 which engages a refractory supporting disc 61 having adiameter somewhat less than half that of the refractory plate. A bolt 68extends through the sleeve and the bore, the head of the bolt resting onthe shoulder 63, and a nut bears on the lower face of the base H wherebythe unit may be held together. In practice the nut 66 is tightened sothat the refractory plate I2 is snugly held between the disc 61 and thecover which engages the annular portion 5| of the refractory. There isnot, however, any appreciable compression stress in the refractoryplate. It is only necessary to hold the refractory plate on the sleeveagainst the jars and shocks of assembly and shipping operations. Noattempt is made to confine the plate, with this mechanism, against heatexpansion forces. The side walls of the recess 62 carry all utensilloads and brace the cover portion 58 so that it cannot transmit loads tothe portion- .of the plate [2.

When the nut 65 is tightened the flange 59 of the cover, resting on thelugs 44 attached to the base, is forced upwardly at its perimeter untilthe convex cover has become substantially plane. When this has occurredthe cover plate: engages the annular portion 5| of the refractory onlylightly, it being unnecessary and undesirable to have any compressionforce applied at this point; The sleeve '64 has a greater heat expansionthan the refractory disc, so that load transmission to the refractory isstill further minimized.

At this point it is occasionally helpful to use a washer 10, preferablyof asbestos or other yieldable heat resisting material in order toinsure a yieldable support. Such a washer isillustrated at the left sideof Fig. 4, it being understood that this washer, when used, extendsannularly between the oover and the refractory plate and has an outerdiameter substantially equal to that of the annular portion 5| of therefractory, and an inner diameter substantially equal to the outerdiameter of the conical portion 62.

With this mechanism it is seen that the sleeve is thus a load carryingmeans between the cover and the base in that it transmits loads betweenthese two parts and prevents the application of loads to the plate.

With a mechanism of the type described utensil loads are carried by thecover and transmitted by the cover to the sleeve 64 and, through theflange 59, to the lugs 44, and from the base flange 28 to the stovepanel l0. With this type of construction the refractory is free fromutensil load in spite of occasional deflections of the cover.

It is also noted that the cover when installed on the heater is under adeforming stress due to the fact that the convexity thereof has beenremoved. With a pre-loaded cover of this nature, the heat expansionforces are insufficient to cause bulging, warping or twisting.

It should be noted, however, that the cover is free to expand laterally,the material of the flange 59 merely sliding over the co-planar topedges of the lugs 44. Hence, under no conditions can the refractory besubjected to bending forces inasmuch as its perimeter is spacedvertically and laterally from the cover. 7

When the terminal junction studs 38 are mounted on the base, it will benoted that the refractory cannot be injured by any mechanical forcesapplied to the power connectors 4|.

The radial space between the cover and base flanges 59 and 22respectively, plus the spacing provided by the lugs 44, between thebottom of the flange 59 and the base, allowsventing of the regionbetween the cover-and the base, this venting being limited, however, andoccurring only inside the base flange 22.

It will benoted that the base has two flanges only one of which makescontact with the top panel In, and then only through a small number ofscattered bosses 26 between which additional venting may occur.Consequently heat cannot be readily conducted from the heating elements43 to the top panel l0 and this is particularly advantageous where thetop panel is covered with a material which cannot readily stand wideranges of temperature change. It will also be noted that, when thisheater unit is installed in the top panel Hi there areno exposed metaledges to scratch the utensils.

Although the invention has been described in connection with a specificembodiment, the principles involved are susceptible of numerous otherapplications which will readily occurto persons skilled in the art. Theinvention is, therefore, to be limited only as indicated by the scope ofthe appended claims.

I claim:

1. In combination, a base, a refractory plate having-a heating elementassociated therewith, a cover comprising a convex top and a dependingflange portion extending circumferentially 0f said plate, and connectionmeans for deforming said cover and securing it to said base, said cover,when deformed, having a substantially plane top.

2. In a heating unit, a base member having a peripheral flange, a covermember having a peripheral flange, said members being disposed inconfronting relation with their flanges telescoped and spaced apart, aheating element disposed between said members, spaced lugs carried bythe member having its flange disposed outermost to form an abutment forslidingly engaging the edge of the innermost flange, whereby the membersare maintained spaced apart but are free for radial expansion andcontraction, and means for maintaining said members against separation.

13. In combination, a base structure, a refractory plate, a heatingelement associated with said plate, a cover for said plate having aconvex form, means on said base structure defining an abutment for theperiphery of said cover, and means for securing said cover to said baseand applying pressure substantially at the center of the cover to forceit against the abutment and cause it to assume a substantially planarform.

THOMAS E. DADSON.

